When is a pepper not a pepper?
Have you ever wondered what the relation between the ground black peppercorns in a pepper shaker is to the chili peppers and bell peppers on the plate? Turns out, they're pretty much unrelated, aside from both being plants and from planet Earth.
Black (and white or green, for that matter) peppercorns (Piper nigrum) are a member of the Piper genus, and are native to South and South-East Asia. Peppercorns were one of the many luxury spices that came across the Eurasian continent on caravans, at least as far back as the Greek empire.
Like the other spices, they were relegated solely to the rich, and were used for medicinal purposes as well as in cooking. Black and long pepper (Piper longum) were used in treatments for diarrhea, cholera, constipation, hoarseness, gangrene, hernia, heart disease, insomnia, joint pain, sunburn, and tooth abscesses.
The active piquant compound in black pepper is called piperine, and while it is structurally and evolutionarily unique from the piquant compound in chili peppers (capsaicin), it interacts with the tastebuds in a way that triggers the same chemical pathways to the brain.
This similarity, in fact, is why chilies (Capsicum) are known as "chili peppers" - when Christopher Columbus brought the first chilies back to Europe in 1493, the warming, spicy taste that chilies imparted led to them being classified in the same group as black pepper. We now know that the "peppers" found in the New World belong to the family Solanaceae, and are related to deadly nightshade, potatoes, tomatoes, and tobacco, among many other economically and pharmacologically important plants. Black pepper, meanwhile, is distantly related to magnolias, but otherwise in a group of relative-unknowns.
The sweet peppers or bell peppers are a close relative to the chili peppers, but are unique in the Capsicum genus in that they do not produce capsaicin, and as such are not "hot" like the others. By the way, what's the difference between red and green bell peppers? Nothing but age! They're the same species - a cultivar of Capsicum annum, which happens to be naturally somewhat hot. You won't find a bell pepper in the wild, as they were developed by humans!
Images: Top: Spices, Their Nature and Growth. McCormick and Co., 1915. Depicting Capsicum, chilies, and peppercorn varieties. Bottom Left: Köhler's Medizinal-Pflanzen in naturgetreuen Abbildungen mit kurz erläuterndem. 1885. Capsicum annum. Bottom Right: Köhler's Medizinal-Pflanzen in naturgetreuen Abbildungen mit kurz erläuterndem. 1885. Piper nigrum.